The difficulties of 24-hour urine collection are well recognized, especially for elderly people for whom a means of estimating protein excretion from a single casual unit sample would be preferable. We compared measurement of total urinary protein estimated by the protein/creatinine ratio with 24-h urine collection and examined the role of the ratio in discriminating between clinically important levels of proteinuria. Although the protein/creatinine ratio appeared to have an excellent correlation with the 24-h collection, the absolute agreement between the two methods was poor. However, the clinical role of the protein/creatinine ratio as a semi-quantitative test of proteinuria remained, provided adjustment for expected creatinine excretion was made.